1. Field of the Invention
The present invention relates to a control of a running condition of an automobile, and more particularly, to speed stage shifting of an automatic transmission of an automobile.
2. Description of the Prior Art
It is already known to shift the speed stages of the automatic transmission according to a selection between a power shift pattern prepared with a preference on the power performance of the automobile to the fuel consumption thereof and an economy shift pattern prepared with a preference on the fuel consumption of the automobile to the power performance thereof as described in, for example, U.S. Pat. No. 4,733,580 assigned to the same assignee as the present application. The selection between the power shift pattern and the economy shift pattern has been conventionally generally left to the manual switching operation by the driver.
In Japanese Patent Application 62-304779 (Laid-open Publication 1-145457) assigned to the same assignee as the present application, it has been proposed to control an automatic transmission of an automobile including a main speed change gear mechanism and an auxiliary speed change gear mechanism connected in series to provide a plurality of speed stages, particularly in accordance with the load on the automobile so that, in addition to a standard speed stage shifting of the automatic transmission based upon vehicle speed and throttle opening, the auxiliary speed change gear mechanism is shifted down when the load on the vehicle is greater than a standard load expected to be imposed by a driver or a driver and a companion, in order to improve the power performance of the automobile in a high load condition imposed by a join of more passengers and/or baggages, while ensuring a high economy performance in the normal use of the automobile under the normal load. Although this idea will be effective in automatically harmonizing the power performance and the economy performance of the automobile, there is a difficulty in detecting the load at high reliability with less costs for load sensing equipments, because, although the load on the automobile would be detected at the suspension of the vehicle body by a vehicle wheel, since the load on the vehicle generally shows a high variety in the distribution thereof on the four wheels, load sensing means would be required at all four vehicle wheel suspensions.
On the other hand, in Japanese Patent Laid-open Publication 62-198522, it has been proposed to control a steering performance of an automobile so that the yaw rate in the steering of the automobile follows a standard performance predetermined to be desirable therefore by controlling the distribution of the driving torque between the front vehicle wheels and the rear vehicle wheels in a four wheel drive vehicle and between a left rear vehicle wheel and a right rear vehicle wheel in a rear wheel drive vehicle. This prior art is based upon the recognition that a steering performance such as the so-called oversteering or understeering of the automobile can be changed according to a change of distribution of the driving torque between the front and rear vehicle wheels or between the rear left and rear right vehicle wheels.